Capacitors are common devices used in electronics, such as integrated circuits, and particularly semiconductor-based technologies. Two common capacitor structures include metal-insulator-metal (MIM) capacitors and metal-insulator-semiconductor (MIS) capacitors. One important factor to consider when selecting a capacitor structure may be the capacitance per unit area. MIS capacitors may be advantageous since a first electrode as the semiconductor may be formed of hemispherical grain (HSG) polysilicon that exhibits a higher surface area in a given region compared to a planar surface of amorphous polysilicon. The higher surface area provides more capacitance per unit area occupied by a capacitor.
However, a high K factor (also known as dielectric constant or “κ”) dielectric material may be desirable to further enhance capacitance. Ta2O5 is one example of a high K factor dielectric, but it inherently forms an interfacial dielectric layer of SiO2 when formed on a capacitor electrode comprising HSG. The interfacial dielectric exhibits a lower K factor than Ta2O5 and thus reduces the effective dielectric constant for the capacitor construction. Such reduction may be significant enough to eliminate any gain in capacitance per unit area otherwise achieved by using HSG instead of a planar electrode. Use of other oxygen containing high K dielectric materials has proved to create similar problems.
Because it may be desirable to provide area enhancement of an electrode in a MIM structure using HSG, one attempt at addressing the stated problem is forming a silicon nitride insulative barrier layer over the HSG. The silicon nitride barrier layer may be formed by nitridizing the silicon of the outer surface of HSG. Unfortunately, silicon nitride exhibits a K factor of only about 7, less than the K factor of some high K factor dielectrics that are desirable. Accordingly, even the silicon nitride barrier layer reduces the effective dielectric constant of the capacitor.